Abstract
Despite significant scientific advances, the nature of the left-hemispheric systems involved in language (speech and gesture) and manual actions is still unclear. To date, investigations of human laterality focused mainly on non-communication functions. Although gestural laterality data have been published for infants and children, relatively little is known about laterality of human gestural communication. This study investigated human laterality in depth considering non-communication manipulation actions and various gesture types involving hands, feet, face and ears. We constructed an online laterality questionnaire including 60 items related to daily activities. We collected 317 594 item responses by 5904 randomly selected participants. The highest percentages of strong left-lateralized (6.76%) and strong right-lateralized participants (75.19%) were for manipulation actions. The highest percentages of mixed left-lateralized (12.30%) and ambidextrous (50.23%) participants were found for head-related gestures. The highest percentage of mixed right-lateralized participants (55.33%) was found for auditory gestures. Every behavioural category showed a significant population-level right-side bias. More precisely, participants were predominantly right-lateralized for non-communication manual actions, for visual iconic, visual symbolic, visual deictic (with and without speech), tactile and auditory manual gestures as well as for podial and head-related gestures. Our findings support previous studies reporting that humans have left-brain predominance for gestures and complex motor activities such as tool-use. Our study shows that the Rennes Laterality Questionnaire is a useful research instrument to assess and analyse human laterality for both manipulation and communication functions.
Highlights
Brain lateralization has been the subject of a substantial body of the literature for many years
We studied humans’ laterality for both non-communication and communication functions associated with diverse daily activities
Our results evidence that each of the nine behavioural categories we considered present a right-side bias at the population level
Summary
Brain lateralization has been the subject of a substantial body of the literature for many years (e.g. see [1] for review). An increasing number of studies of different species support the hypothesis that behavioural lateralization would have been selected, because it provided significant advantages at both the individual and population levels [2,3]. Lateralization would have appeared at the individual level because it enhanced brain efficiency [4]. Population-level lateralization would have emerged because it favoured social coordination between asymmetrical organisms (e.g. shoaling fish: [5]). Laterality patterns at the population level would be more prominent for social species than for solitary species (e.g. fish: [6]; tadpoles: [7]). Social pressures would have shaped laterality through natural selection, as recently supported by gestural studies (chimpanzees and gorillas: [8,9]; humans: [10])
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